INSTITUTO SUPERIOR TÉCNICO Universidade Técnica de Lisboa REHABILITATION OF FLEXIBLE PAVEMENTS THROUGH RECYCLING WITH CEMENT Filipe Goulart de Medeiros Reis Batista Extended Abstract to obtaining the Master Degree in Civil Engineering Lisbon October 2009
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INSTITUTO SUPERIOR TÉCNICO
Universidade Técnica de Lisboa
REHABILITATION OF FLEXIBLE PAVEMENTS
THROUGH RECYCLING WITH CEMENT
Filipe Goulart de Medeiros Reis Batista
Extended Abstract to obtaining the Master Degree in
Civil Engineering
Lisbon
October 2009
1
1. Introduction
With the elaboration of this study was intended to evaluate the load capacity of a road
pavement submitted to rehabilitation with resource to cold in situ recycling with cement
technique, and compare it with the load capacity of the same pavement, this time submitted to a
normal reinforcement with bituminous mixtures. The results were obtained from load tests with a
Falling Weight Deflectometer (FWD) device, and were interpreted having in account the effects
of climatic conditions in which they were made, particularly the air temperature and the
temperature of bituminous layers. The tests performed allowed to characterize the mixtures
from the point of view of their stiffness, fatigue and permanent deformation.
2. Road Pavements Structural Behaviour
2.1. General Considerations
The main road pavement function is to ensure a free and unwrapped rolling surface that
allows the circulation of vehicles in security, comfort and economic conditions, during pavement
lifetime and being submitted to different traffic levels and a variety of climatic conditions.
According to the way in which we may associate layers formed by different types of
materials, so results different types of pavements, which present different types of behaviours
when requested by different traffic levels in combination with climatic conditions which they
were submitted. Depending on the type of materials and its stiffness three pavement types can
be distinguished. Flexible pavement using bitumen as a binder, rigid pavement using cement as
a binder and semi-rigid pavement using bitumen and cement as a binder [1].
2.2. Quality Control
Together pavement and subgrade structural capacity can be evaluated in accordance
with certain parameters, of which special mention is made to the surface vertical deflection,
which is considered as the response from the pavement to the intensity of loads under certain
conditions [1].
Among the equipment designed to study the deflections of pavements, only the Falling
Weight Deflectometer (FWD) was considerate, because it was the device used in the bearing
capacity evaluation of the case study pavement. With the application of these non-destructive
load tests, the establishment of structural behaviour models for each study areas was intended.
The most used design model for this purpose is the Burmister model.
The establishment of a pavement structural behaviour model involves not only the
estimate of layers stiffness moduli, but also the adoption of a thickness soil top layer, since
usually it becomes necessary to subdivide the subgrade soil into two layers, a top layer more
deformable, which in the case study was adopted 2,5 meters, and another layer under the first
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one, with a semi-infinite thickness, designated by rigid layer with a significantly higher stiffness
module than the first one [2].
3. Flexible Pavements Structural Rehabilitation
3.1. Strengthening of Flexible Pavements
The term pavement strengthening is referred as signifying the action or actions capable
of increasing the structural capacity of an existing degraded pavement, and support, together
with the subgrade, the loads caused by the passage of vehicles under certain conditions of
application [1]. A possibility is the application of one or several bituminous overlays, another
possibility may consist of milling the cracked layers and their replacement by applying new
layers, aiming to adjust the pavement to the new traffic demands, and prevent the reflection of
existing deterioration to the new surface course.
3.2. Pavement Recycling
The main purpose of road pavements recycling is to transform one or more layers of a
deteriorated pavement into a homogeneous layer adapted to the new traffic demands. This
technique consists in the reuse of the milled material and their application in the construction of
a new layer, usually a base course that represents the new pavement main structural layer.
Considering aspects like the place of recycling, the production temperature of the
recycled mixture and the used binder, thus can be defined several recycling processes [3]:
Cold in plant recycling with bituminous emulsion.
Cold in plant recycling with foamed bitumen.
Semi-hot in plant recycling with bituminous emulsion.
Hot in plant recycling with bitumen.
Cold in situ recycling with cement.
Cold in situ recycling with bituminous emulsion.
Cold in situ recycling with foamed bitumen.
Hot in situ recycling with bitumen / additives.
4. Cold in situ Recycling with Cement
4.1. General Considerations
Of the milled layers mixture with cement results in a new layer as like an extensive
grading aggregate treated with cement (AGEC), which presents a higher bearing capacity than
any of the previously existing [1]. The pavement that initially was flexible will become semi-rigid.
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4.2. Description of the Constructive Process
The execution of this process includes the following operations [4] [5]:
Prior study of the old pavement material and study of the mix design for
obtaining the working formula for each distinct characteristics section.
Mix the milled surface course material with water (optimal content), cement,
additives (for improvement of recycled material characteristic) and aggregates
(for grading correction of the final recycled mixture).
Laying and pre-compaction with a steel wheel roller to avoid humidity losses
Levelling and profiling the treated material with a grader.
Compaction the profiled mixture to acquire the optimal density with a pneumatic
tyre roller.
Cure treatment of the recycle mixture for its protection.
In Figure 4.1 is shown the sequence of elementary tasks [5].
Figure 4.1 – Sequence of elementary tasks [5]
4.3. Pavements Design Methodologies Using Layers with Addition of
Cement
Semi-rigid pavement in general, in terms of design, is treated like a flexible pavement.
However, the existence of a rigid base course that includes the mixture of recycled material with
cement reduces the stresses on the subgrade leading to an improbable permanent deformation
occurrence, which exists in flexible pavements. For that, generally, permanent deformation is
not a considered state limit of ruin.
With the purpose of calculating stress and strain states of the pavement, and using the
most relevant of these values, the admissible numbers of passages by the standard axle 𝑁130 𝑘𝑁
that the pavement can support, three main criteria of design limit states of ruin were used.
The Shell criteria for design limit states of ruin:
Shearing by fatigue on the basis of bituminous layers criteria:
𝜀𝑡 = 0,856𝑉𝑏 + 1,08 × 𝐸𝑀𝐵−0,36 × 𝑁130𝑘𝑁
−0,2 (4.1)
𝑁130 𝑘𝑁 – Accumulated number of passages of the standard axle;
𝜀𝑡 – Maximum traction stress induced by the standard axle;
𝑉𝑏 – Bitumen volumetric percentage;
𝐸𝑀𝐵 – Stiffness moduli of bituminous mixtures (Pa).
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Permanently deformed on the top of the subgrade criteria (this criteria is
generally not considered in this type of pavement, but it’s of great importance in
flexible pavements):
𝜀𝑧 = 1,8 × 10−2 × 𝑁130𝑘𝑁−0,25 (4.2)
𝜀𝑧 – Maximum vertical compression strain at the top of the subgrade.
And the shearing by fatigue at the bottom of mixtures of materials with hydraulic binders
criteria, which is considerate of great importance in flexible pavements:
𝜎𝑡
𝜎𝑟
= 1 + 𝑎 log 𝑁130𝑘𝑁 (4.3)
𝜎𝑡 – Maximum tensile stress induced by the standard axle (from
ELSYM5 program);
𝜎𝑟 – Resistance to traction under bending (Rbending);
𝑎 – Constant, which depends on the mix composition and properties,
admitting values ranging -0,06 to -0,1.
5. Recycling With Cement Application Study on
Rehabilitation of EN 226
5.1. General Considerations
This chapter presents the case study, concerning pavement structural rehabilitation of
National Road 226 (EN 226), located in the district of Viseu, in which a recycling with cement
technique was applied (designated by B solution) in the worse part of the pavement, and an
overlay reinforcement with new bituminous mixtures in the remaining extension (A solution).
Comparison of the bearing capacity of the pavement section that was submitted to
rehabilitation with resource to cold in situ recycling with cement, obtained of load tests with a
FWD device, with the bearing capacity of the same section of pavement, only this time
submitted to normal overlays reinforcement with new bituminous mixtures that previously were
used in the better sections of the EN 226, was carried through.
Evaluated the pavement before rehabilitation two zones were chosen and were
distinguished by presented the degree of degradation (zone 1 between km 14+000 and km
43+000 that appeared less degraded and zone 2 between kms 46+000 and 64+000, that
presented a widespread degradation) [6], the next step was to find the solutions that ensure
proper conservation/rehabilitation of the pavement.
For zone 1, particularly the extension in study between km 38+000 and km 40+000
designated Solution A, it was opted to use an overlay reinforcement with new bituminous
mixtures, like the structure illustrated in the Figure 5.1
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Figure 5.1 – Pavement structure for solution A (km 38+000 to km 40+000)
Throughout the zone 2, designated Solution B, it was considered the recycling of all the
extension of the pavement. The new pavement structure presents an in situ recycled layer with
4% addition of cement in a thickness of 20 cm (base course with high mechanical strength), on
top of it was applied a Stress Absorbing Membrane Interlayer (SAMI), in order to reduce the
crack propagation phenomenon and to promote bonding with the following layer. The pavement
structure solution is illustrated in Figure 5.2.
Figure 5.2 – Pavement structure for solution B (km 46+000 to km 64+000)
5.2. Pavement Load Capacity after Rehabilitation
Load tests were performed with a Falling Weight Deflectometer device in each one of
the directions (D1 and D2), since pavements in the external rutting area may present distinct
behaviours. The campaign took place between 24 and 26 June 2008. Initially, in each point, the
load cell was adjusted to the pavement surface. With a second impact, being the drop height set
to match the desired peak load, the deflections were measured. The peak load applied by the
LNEC device was 65 kN, because it´s the value that simulate the standard axle of 130kN.
The pavement deflections induced by the impact load were measured at various points
through geophones supported on the surface of the pavement. The distances from start point
are located: D0 - 0 m; D1 - 0.30 m; D2 - 0.45 m; D3 - 0.6 m; D4 - 0.9 m; D5 - 1.2 m; D6 - 1.5 m; D7
- 1.8 m; D8 - 2.1m. The Figure 5.3 illustrates the FWD load tests.
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Figure 5.3 – Deflection obtained from start point[7]
With deflection values measured its normalization is realized, since that exist tiny impact
forces variations in each point. The normalization is given by the following expression (5.1):
Coimbra. [2] – ANTUNES, M. L., 1993. Avaliação da Capacidade de Carga de Pavimentos
Utilizando Ensaios Dinâmicos. Tese Elaborada no LNEC e Submetida para Obtenção do Grau de Doutor em Engenharia Civil pela Universidade Técnica de Lisboa, IST. Outubro de 1993. Lisboa.
[3] – MARTINHO, F., 2005. Reciclagem de Pavimentos – Estado da arte, Situação Portuguesa e Selecção do Processo Construtivo. Tese de Mestrado. Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
[4] – SEIXAS, P., 2008. Reciclagem de Pavimentos com Espuma de Betume - Uma Experiência a Grande Altitude – Cordilheira dos Andes, Peru. V Congresso Rodoviário Português. Estrada 2008. Centro de Congressos do Estoril, Portugal, 12 a 14 de Março de 2008.
[5] – TRINDADE, M., 2007. EN 226 Beneficiação entre Lamego e a Ponte do Abade. Comunicação Direcção de Estradas de Viseu. Estradas de Portugal E.P.E., 29 a 30 de Novembro de 2007.
[6] – I.E.P. (actual E.P.), 2005. E.N. 226 - Beneficiação entre Lamego e a Ponte do Abade. Instituto de Estradas de Portugal (actual Estradas de Portugal). Direcção de Estradas de Viseu.
[7] – ANTUNES, M. L.; MARECOS, V., 2008. Ensaios de Carga com Deflectómetro de Impacto na EN226 entre Lamego e a Ponte do Abade. LNEC. Agosto de 2008. Lisboa.
[8] – AASHTO, 2001. Guide for Design of Pavements Structures. AASHTO, American Association of State Highway and Transportation Officials. Washington, DC. 2001. USA.
[9] – MOLENAAR, A. A. A., 1994. State of the Art of Pavements Evaluation. Proceedings. The 4
th International Conference on the Bearing Capacity of Roads and Airfields. Vol. 2.
Minneapolis, 1994. [10] – FREITAS, E. F.; PEREIRA, P. A. A.,2001. Estudo da Evolução do Desempenho dos
Pavimentos Rodoviários Flexíveis. Universidade do Minho. Azurém. Guimarães. [11] – STUBSTAD, R. N.; LUKANEN, E.O.; RICHTER, C.A., BALTZER, S., 1998.
Calculation of AC Layer Temperatures From FWD Field Data. The 5th International
Conference on the Bearing Capacity of Roads and Airfields. Trondheim. July 1998. [12] – NEVES, J., 2008. Folhas da Disciplina de Construção e Manutenção de Infra-
Estruturas de Transportes, Instituto Superior Técnico, Lisboa. [13] – RODRIGUES, B., 2008. Reciclagem “In Situ” com Adição de Cimento - O Caso de
Estudo da E.N. 226. Dissertação para Obtenção de Mestre em Engenharia Civil na Especialidade de Urbanismo, Transportes e Vias de Comunicação. Faculdade de Ciências e Tecnologia. Universidade de Coimbra - FCTUC, Coimbra.
[14] – JAE (actual EP – Estradas de Portugal), 1995. Manual de Concepção de Pavimentos para a Rede Rodoviária Nacional.